Globus pallidus
The globus pallidus (Latin for "pale globe") is a sub-cortical structure of the brain. It is a major element of the basal ganglia system. In this system, it is a major constituent of the basal ganglia core, which consists of the striatum and its direct targets: globus pallidus and substantia nigra. The last two are made up of the same neuronal elements, have a similar main afferent (the dorsal striatum), have a similar synaptology, and do not receive cortical afferents. It was recently discovered http://news.bbc.co.uk/1/hi/health/7132829.stm to play an active part in pre-filtering external stimuli and may help reduce the amount of irrelevant information the brain needs to store. History of name The origin of the name is not established. It was known by Dejerine (1906) but not by Santiago Ramón y Cajal (1909-1911). As the elements in no way have the shape of a globe, Foix and Nicolesco (1925), the Vogts (1941), Crosby et all.(1962) followed by the Terminologia anatomica proposed the simpler term (neuter adjective) of pallidum (pale). During a long period the globus pallidus was unduly linked to the putamen in the lentiform nucleus (nucleus lenticularis or lentiformis). This was a heterogeneous anatomical entity that is part of the striatum rather than the pallidum. The link with the substantia reticulata was stressed very early on due to the similarities in dendritic arborisation, but in spite of solid arguments this link is still not widely accepted. The two however constitute a particular set of the basal ganglia system (the pallidonigral set). Parts In primates, the dorsal pallidum, or globus pallidus, is divided into two segments by the medial medullary lamina. A frequent nomenclature uses the adjectives internal and external to refer to the two divisions of the globus pallidus. The medial segment of the dorsal pallidum, internal globus pallidus (GPi), and lateral division of the dorsal pallidum, external globus pallidus (GPe), are thus the two parts of the dorsal pallidum that are two closed nuclei surrounded everywhere by myelinic walls. The ventral pallidum lies within the substantia innominata (Latin for un-named substance) and receives efferent connections from the ventral striatum (nucleus accumbens and olfactory tubercle). The ventral pallidum projects to the dorsomedial nucleus of the dorsal thalamus, which projects to the prefrontal cortex. The ventral pallidum also projects to the pedunclopontine nucleus and tegmental motor area. The function of the ventral pallidum is limbic-somatic motor interface for the planning and inhibition of movements from the dorsal striatopallidal complex. Structure Pallidal nuclei are made up of the same neuronal components. In primates, almost all pallidal neurons are very large, parvalbumin positive, with very large dendritic arborizations. These have the peculiarity of having the three-dimensional shape of flat discs, parallel to one another, parallel to the border of the pallidumYelnik, J., Percheron, G., and François, C. (1984) A Golgi analysis of the primate globus pallidus. II- Quantitative morphology and spatial orientation of dendritic arborisations. J. Comp. Neurol. 227:200-213 and perpendicular to the afferent striatopallidal axons.Percheron, G.,Yelnik, J. and François. C. (1984) A Golgi analysis of the primate globus pallidus. III-Spatial organization of the striato-pallidal complex. J. Comp. Neurol. 227: 214-227 There are only a few small local circuitry neurons. The globus pallidus is traversed by the numerous myelinated axons of the striato-pallidonigral bundle that give it the pale appearance from which it is named. The ultrastructure is very peculiar, as the long dendrites are everywhere, without discontinuity, covered by synapses.Fox, C.A., Andrade, A.N. Du Qui, I.J., Rafols, J.A. (1974) The primate globus pallidus. A Golgi and electron microscopic study. J. Hirnforsch. 15: 75-93di Figlia, M., Pasik, P., Pasik, T. (1982) A Golgi and ultrastructural study of the monkey globus pallidus. J. Comp. Neurol. 212: 53-75 Pallidonigral pacemaker The two pallidal nuclei and the two nigral (pars compacta and pars reticulata) parts constitute a high-frequency autonomous pacemakerSurmeier, D.J., Mercer, J.N. and Savio Chan, C. (2005) Autonomous pacemakers in the basal ganglia: who needs excitatory synapses anyway? Cur. Opin.Neurobiol. 15:312-318. (see primate basal ganglia system#Pallido-nigral_set_and_pacemaker) Common afferences The two parts receive successively a large quantity of GABAergic axonal terminal arborisations from the striatum through the dense striato-pallidonigral bundle. The synaptology is very peculiar (see primate basal ganglia system).The striatal afference contribute for more than 90% of synapses. The two pallidal nuclei receives dopaminergic axons from the pars compacta of the substantia nigra. , globus pallidus (GPe and GPi) CAUDAL: subthalamic nucleus (STN), substantia nigra (SN)]] See also *Lentiform nucleus References Additional images Image:Gray718.png|Coronal section of brain through intermediate mass of third ventricle. Image:Gray744.png|Coronal section of brain through anterior commissure. Image:Telencephalon-Horiconatal.jpg|Horizontal section of right cerebral hemisphere. Image:Basal-ganglia-classic.png |Connectivity Diagram showing glutamatergic pathways as red, dopaminergic as magenta and GABA pathways as blue. Image:Pallidus.jpg|Horizontal slice of MRI-image showing the globus pallidus. External links * * * * Diagram at uni-tuebingen.de Category:Basal ganglia Category:Cerebrum